The present invention relates to a device suitable for obtaining a scanning image of a sample on the basis of an information signal, peculiar to the sample, obtained by emission of an electron beam to the sample.
A method for observing a sample at high resolution using a scanning electron microscope or the like has been described in Japanese Patent Laid-open No. Sho 57-172643, in which a lens magnetic field is generated at a lower portion of an objective lens; a secondary electron generated from the sample is accelerated by a positive voltage applied to electrodes disposed on an objective lens portion; and the secondary electron is detected at a portion over the objective lens. On the other hand, a so-called retarding method is intended to decelerate a primary electron directly before a sample by applying a negative voltage to the sample. Even in this retarding method, a secondary electron generated from a sample is accelerated by a voltage applied to the sample and advances over the objective lens, and thereby it must be detected at a portion over the objective lens. In each method, an electric field is generated between the sample and the objective lens.
In the above-described prior art methods, when a conductive sample is tilted, an axisymmetric property of an electric field between a sample and an objective lens is put into disorder, and consequently a lateral electric field component is generated on the optical axis of the electron beam. This is inconvenient in increasing astigmatism, thereby making poor resolution. The disorder of the axisymmetric property of an electric field also disturbs the orbit of a secondary electron generated from the sample, and obstructs effective arrival of the secondary electron at a detector disposed over the objective lens. This results in lowering of the detection efficiency of the secondary electron.